Galileo Found ThemYou Can See ThemJupiters Moons

A treat for any stargazer is Jupiter's
moons. With four of the six largest natural satellites in the Solar
System these objects are easy to spot.

With apparent magnitudes ranging from
4.6 to 5.6 during Jupiter's opposition these satellites are big and
bright.

If not for the brightness and glare
from Jupiter itself these moons could easily be seen with the naked
eye.

Small binoculars bring them into focus
easily.

Io and Europa would be the toughest to spot because of their closeness to Jupiter.

Ganymede and Callisto at maximum
separation from the planet offer the best chance to catch a naked-eye
glimpse.

Galileo Galilei discovered them on the
nights of January 7th and 8th 1610. A second
astronomer named Simon Marius claimed to have found them earlier but
he and Galileo were using different calendars at that time. When
comparing the Julian calendar that Marius was using to the Gregorian
calendar Galileo was using the dates coincide.

Galileo published his findings first
and receives credit for the discovery. A Chinese astronomer in 325
mentions Jupiter's moons in his writings as well.

Simon Marius with suggestions from
Johannes Kepler named the satellites in 1614. These names were not
widely used until the 20th century. Until then they were
simply known as Jupiter I-IV.

The four Galilean moons are all over
1,900 miles in diameter and one, Ganymede is larger than the planet
Mercury. The fifth of Jupiter's moons, Amalthea was the last moon
discovered by direct observation.

E. E. Bernard found it in 1892. All
moons since then have been found from telescope pictures and
satellites.

This is a picture of Jupiter's moons taken through a 10in(250mm) telescope. This should give you an idea of what looking through a scope is like.

IO

Orbiting the planet in about 42 hours
as seen from Earth. It is the 4th largest moon in the
Solar System.

With over 400 active volcanoes, Io is
the most geologically active body in the Solar system. Many of the
mountains on the surface are taller than Mount Everest.

Io has a thin atmosphere composed
primarily of sulfur dioxide.

Europa

Apparent Magnitude:5.29

Second from the planet of the large
moons is Europa.

The smallest of the four main Jovian
satellites, Europa is the 6th largest moon in the Solar
System just after the Moon itself.

Orbiting Jupiter in about 3.5 days it
takes twice as long as Io to orbit and half the time as Ganymede.

With its oxygen atmosphere and possible
liquid ocean under the surface, scientist think that Europa could be
a place to find life in outer space if it exists.

Ganymede

Apparent Magnitude:4.61

Third in line is the big daddy of
satellites...Ganymede.

Named after the mythological cup bearer
to the gods Ganymede is the largest moon in the Solar System. Bigger
around than Mercury though not as dense.

Orbiting Jupiter in 7 days, Ganymede is
in an orbital sync with Io and Europa. Every orbit of Ganymede is
matched by two by Europa and four by Io.

Contains a thin oxygen atmosphere.

Callisto

Apparent Magnitude: 5.65

The fourth natural satellite of the
quartet is Callisto.

The 3rd largest moon behind
Ganymede and Saturn's Titan.

Farther away from the planet and not
locked into an orbital sync with the other three, Callisto orbits in
16 Earth days.

A thin carbon dioxide atmosphere
doesn't protect Callisto from impacts and the surface is heavily
cratered. Callisto does have an ionosphere.

Also possibly containing a liquid ocean
under the surface. Callisto is not affected as
much as the other moons by Jupiter's intense radiation and scientist
think that it could be used someday as a base for space exploration.